The invention relates to an arrangement for cooling electronic components and/or assemblies.
The development of electronics and primarily the development of electronic components, since the use of semi-conductor technology, has been characterized in that both the components and the assemblies, including a plurality of components and devices in which the components/assemblies are installed, are becoming increasingly small.
Conventionally, electronic components and assemblies are applied by so-called Surface Mounted Technology (SMT) or by so-called Through Hole Technology (THT) onto a substrate which is also denoted as a printed circuit board. The substrate in this case is a carrier for electronic components and assemblies which are fastened mechanically to the substrate during the mounting process, for example by so-called reflow soldering. The substrate also has the necessary electrical connections—so-called printed conductors—for the circuits formed of the components and/or assemblies. One or more substrates populated with components and/or assemblies are then installed in a housing and together form therewith an electronic device which is able to be accommodated in a retaining device.
A widely-used retaining device for electronic devices is, for example, a so-called 19-inch rack. Said rack is a frame for electronic devices with a standard width of 19 inches, wherein the individual devices which are able to be mounted in said rack have a front plate width of 46.26 cm. A so-called vertical unit of said rack is fixed at 4.445 cm or 1.75 inches, wherein a rack generally has a plurality of vertical units. In computer centers, for example, racks having a height of 2 meters are often used, comprising, for example, 42 vertical units. The standards which refer to 19-inch racks are, for example, EIA 310-D, IEC 60297, DIN 41494 SC48D, etc. By standardizing the rack, any electronic devices may be installed in the rack provided they also correspond to the standards or dimensions set therein.
Due to the specifications set by the holding frame, electrical devices and substrates populated therewith are manufactured to suit this rack format. This results in a set height for the device and thus also for the design and population of the substrate. The components and assemblies are thus constructed horizontally, i.e. a substrate conventionally has only one side populated by components and/or assemblies—the so-called populating side.
During the operation of electronic components and/or assemblies, the limited efficiency thereof results in a power loss which is conventionally dissipated in the form of heat. This is highly significant, in particular in power electronic components (for example relays, thyristors, converters, etc.). Heat dissipation is, however, also becoming increasingly significant in semi-conductor electronics, such as for example integrated circuits (IC), transistors, diodes, field effect transistors, etc.—in particular in so-called deep-submicron semi-conductor components which have a relatively high standby current and thus corresponding heat generation. Heat may also be generated in printed conductors of the substrate, for example due to high currents and/or in capacitors, for example at high frequencies.
A high degree of electronic integration, for example due to the design of the device and/or restrictions for a fan, such as for example in so-called embedded systems, may lead to a temperature rise in components and/or assemblies which may already have an effect on the reliability of the device, even with a relatively low power loss of the components or assemblies. In order to prevent malfunctions by the heat generation or power loss of the components and/or assemblies, a corresponding cooling or dissipation of the heat has to be ensured. This is important, primarily in areas such as for example satellite technology, where a high degree of reliability of the devices is important.
To a certain extent, the heat loss of the components and/or assemblies may be dissipated from the substrate itself. The substrate, which is formed of an electrically insulating material (for example fiber-reinforced plastics material, etc.) and which, for example, has a high level of copper due to the electrical connections applied, thus functions as a so-called heat sink, for example. With a greater thermal power loss of the components (for example power electronic components, etc.) the substrate is, however, usually no longer adequate as a heat sink in order to discharge the heat and thus to ensure correct operation.
Thus, with greater thermal power losses, for example—according to the so-called bottom-side cooling principle—a separate heat sink is mounted on the side of the substrate remote from the mounted components and/or assemblies. This side of the substrate may thus also be denoted as the heat sink side. The heat losses are thus conducted through the substrate to the heat sink, assisted for example by so-called thermal vias, and discharged thereby for example by thermal radiation and/or convection to a surrounding cooling medium (for example air, etc.). The heat sink conventionally is formed of a metal having good thermal conductivity (for example aluminum, copper, etc.) and generally has a surface discharging the greatest possible amount of heat (for example waves, ribs, etc.). Occasionally, parts of the housing of the electronic device are also used as heat sinks. So-called passive and active heat sinks may be differentiated within the heat sinks.
A passive heat sink primarily acts by convection—i.e. the ambient air is heated and as a result is specifically lighter and rises, whereby an air current is produced and cooler air flows in. However, passive heat sinks—in particular with a horizontal construction of components and/or assemblies—such as for example for devices in 19-inch racks—have the drawback that the heat transport by natural convection is very low, in particular due to the relatively low height. This means that natural convection is not sufficient to prevent malfunctions due to heat losses or a negative impact on the reliability.
In order to achieve improved convection and thus cooling of the components or assemblies—in particular with a horizontal construction—so-called active heat sinks are used. An active heat sink—such as for example described in the publication DE 198 06 978 A1 or in the publication DE 196 53 523 A1—comprises one or more axial fans for producing a corresponding airflow in which a rotational axis of the impeller extends parallel or axially to the airflow. Due to the arrangement of the axial fans (for example to the side of the heat sink, wherein the rotational axis extends parallel to the housing) in a housing of low height, said fans generally have a small diameter and thus have to be operated at a relatively high rotational speed in order to ensure corresponding cooling. A problem when using axial fans is in the relatively high generation of noise. In addition to the noise produced, a drawback has also been shown to be a reduced service life due to the high rotational speed, as well as overheating due to dust, dirt etc. which may lead to breakdown of the fan and thus to malfunctions of the electronic device.
An electronic cooling chassis and/or cooling housing for an electronic device is disclosed in the publication U.S. Pat. No. 4,027,206. In this arrangement, a fan is also fitted in the housing. A cooling medium (for example air) is drawn in through housing openings by said fan and conducted over the electronic components of the electronic device in the housing interior. The fan in this case is oriented with the rotational axis of the impeller axially to the airflow and in this case the fan has a relatively small diameter due to the installation thereof. However, this has the drawback that a relatively high rotational speed for the operation of the fan is required for a corresponding airflow, whereby in addition to high noise generation the service life of the fan is also reduced. Moreover, the fan may overheat due to dust and/or dirt which may lead to breakdown of the fan and to malfunctions and/or damage to the electronic device.
So-called active heat sink arrangements are disclosed in the publication US 2009/0190309 A1 or the publication U.S. Pat. No. 5,663,868. The fans in these publications are also installed as axial fans—i.e. with a rotational axis of the impeller arranged parallel or axially to the airflow. Said fans have a low height due to the installation thereof in the housing and thus have to be operated at a relatively high rotational speed for corresponding cooling. Thus the arrangements disclosed in the publications US 2009/0190309 A1 and/or U.S. Pat. No. 5,663,868 also have the drawbacks of high noise generation and reduced service life of the fan.
In narrow spatial conditions, such as for example in laptops, for cooling graphics cards, processors, etc. in powerful personal computers (PC) or in very compact power electronic units, the so-called heatpipe principle is used. In this case a so-called heat pipe, which is generally produced from copper, transports the heat from the component, from the assembly, from the substrate, etc. to a heat sink. In high performance PC graphics cards—such as for example the “Nvidia GeForce GTX 470” graphics card—for example the heat pipe principle is supplemented by a radial fan arranged to the side of the heat sink and the heat pipe.
This arrangement for the Nvidia GeForce GTX 470 is shown, for example, on the homepage bit-tech.net under <bit-tech.net/hardware/graphics/2010/03/28_nvidia-geforce-qtx-470-1-1280-mb-review/2> or on the Internet page <computerbase.de/artikel/graphikkarten/2010/testnvidia-geforce-gtx-470/3/>. Although the heated air is forced out of the housing by the laterally arranged radial fan, by which air or a cooling medium is drawn in parallel or axially to the drive axis and deflected by 90° by a rotation of the radial impeller and blown out radially, an airflow is not produced for cooling the heat sink and/or the heat pipes. In other words, the air guidance and/or suction action of the radial fan is only partially utilized and barely used for cooling the components, resulting in the risk of the occurrence of so-called hot spots, i.e. hotter areas.